Water reduction mechanism of polycarboxylic ether based superplasticizers
Today'' s concrete superplasticizers are primarily prepared by intensifying different materials such as polycarboxylate water-reducing mommy liquor as well as polycarboxylate slump-preserving mom alcohol plus retarders, air-entraining agents, and defoaming agents. Amongst them, the role of water-reducing mother option in superplasticizer is irreplaceable. Maybe the amount of mother service will alter as a result of the change of concrete product, but I have actually never ever listened to that water-reducing mother remedy is not included in superplasticizer since the sand is also excellent.
The water-reducing mother fluid is made use of as the absolute major product in the water-reducing agent, as well as its feature is to lower the concrete water-cement ratio (indirectly increase the toughness of the concrete), and also at the very same time make certain the fluidness and also workability of the concrete mix, and make sure the toughness of the concrete. At the exact same time, it additionally promotes the job of the building and construction device.
We know that along with seal and water in concrete, the result of the staying materials on the superplasticizer admixture particles is primarily adsorption (waste), so the water decreasing agent is mostly aimed at cement. So initially, let’& rsquo; s discover the hydration process of concrete.
The hydration process of general portland cement is separated right into three stages:
( 1) Dissolution stage: When the concrete touches with water, the surface area of the particles starts to moisten, as well as a small amount of hydration items are produced, which are quickly liquified in water. The revealed new surface allows hydration to continue up until a saturated option of hydration items is developed.
( 2) Gelation stage: As a result of the saturation of the solution, the item that remains to be moistened can no more be dissolved, but is directly precipitated as colloidal particles. With the rise of hydration items, the hydration accumulations, as well as the concrete slurry gradually sheds its plasticity, resulting in a coagulation phenomenon.
( 3) Condensation stage: The colloid composed of microscopic crystals is not stable, and also can slowly recrystallize to create macroscopic crystals, to ensure that the mechanical strength of the solidified body of the cement slurry is constantly boosted, as well as finally it ends up being a concrete rock with a specific mechanical strength.
In the cement slurry, the dispersion device of polycarboxylic ether based superplasticizers is typically considered to be the main duty of steric limitation as well as the secondary duty of electrostatic repulsion. Additionally, the complexation of calcium ions as well as the lubrication of hydration movie also play a role. vital role.
1. Steric barrier:
The hydration procedure of concrete will make the cement molecules draw in each various other, resulting in a flocculation structure.
During the development of the flocculation framework, the cement molecules will certainly encapsulate a part of the water particles, as well as the encapsulated water accounts for about 10% -30% of the overall mixing water (this might be the reason the water minimizing agent has a water lowering price limit). Because it is covered by concrete particles, it can not take part in the free flow and also lubrication in between cement molecules, thus impacting the fluidness of concrete mixtures. When the polycarboxylate concrete admixture molecules initial come into contact with the concrete fragments, the adversely billed main chain in the polycarboxylate concrete admixture molecules can be adsorbed externally of the favorably billed concrete particles, that is, an "anchoring" sensation happens, while the polycarboxylate superplasticizer The lengthy side chain in the particle is prolonged in the fluid stage of the cement slurry to form an adsorption layer with a certain thickness, and also can create a three-dimensional as well as went across long side chain with various other polycarboxylic acid superplasticizer particles expanding in the fluid stage of the cement slurry at the exact same time. Conformation. When the concrete fragments approach each other, the adsorption layer overlaps, and also the bigger the overlapping range, the higher the repulsion between the cement fragments, thereby boosting the dispersibility of the concrete particles. Destroy the flocculation framework in between concrete particles. The release of the water trapped by concrete flocculation can additionally be understood as the water minimizing representative molecules boost the lubricating usage rate of the water molecules to the concrete particles, and also do not raise the water or minimize the number of water molecules out of slim air.
2. The theory of electrostatic repulsion:
Polycarboxylic acid superplasticizer particles include anionic groups (COO2-), as well as in the very early hydration process of concrete, the surface area of cement bits includes favorable fees (Ca2+), as a result, anionic Polycarboxylic acid superplasticizer particles adsorb to favorably billed concrete particles surface. Make the concrete particles right into a "hedgehog" with negative fee. Due to the fact that the cement bits with the very same unfavorable cost drive away each other (electrostatic repulsion), the dispersibility between the concrete bits is improved. At the same time, the adversely billed carboxyl groups and also positively charged calcium ions in the concrete paste kind unsteady complicateds. After the calcium ions liquified in the concrete system are captured, the calcium ion concentration decreases significantly, reducing the calcium ions in the system. It can decrease the formation of gel particles and hence decrease the hydration rate of concrete, prevent the hydration of concrete, and also enhance the dispersion efficiency of cement bits. The better the material of carboxylate ions in the Polycarboxylic acid superplasticizer, that is, the higher the anion cost thickness, the higher the diffusion performance of cement particles (acid-ether ratio). The reduction of calcium ion concentration can inhibit the initial hydration of cement. With the continuous development of hydration, the facility will decay by itself, so Polycarboxylic acid superplasticizer has a particular retarding effect without influencing the strength of concrete.
The branched chain of the polycarboxylic acid superplasticizer particle has hydrophilic teams. These teams create a water film on the surface of the concrete fragments by integrating with water particles, which reduces the surface area energy of the concrete particles. Slips quickly. The mixed result of the above results in splitting up between the concrete fragments. The macroscopic efficiency is that the concrete combination has much better fluidness.
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